[TxMt] Undo should accumulate contiguous input

[David Tolpin]

Hi,

a common practice is to let Undo undo all characters entered during 
last stroke (that is, not interrupted by movements or other operations 
(find/replace/search) at once. That is, If I type a few words, then 
press Option-Z, I expect all the words to disappear, not one letter at 
a time. This is the way undo works in most environments, including 
emacs, vi, TextEdit, AppleWorks, sam, acme, Word ...

David